News | August 11, 2011

Precision Glass & Optics Provides Customized Optical Mirrors For The VIRUS Instrument To Study Dark Energy

Source: PG & O Precision Glass & Optics
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  • The Visible Integral-field Replicable Unit Spectrograph (VIRUS) will be used for the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) to study the mysterious force that is causing the expansion of the universe to accelerate.

Precision Glass & Optics (PG&O), global experts in optical manufacturing and precision thin film coatings, announces the delivery of specialized optical mirrors to Texas A&M University and the University of Texas at Austin for use in building the first-of-its-kind VIRUS instrument, a key part of the Hobby-Eberly Telescope Dark Energy Experiment, or HETDEX. The $36M international research project will study the force that causes the expansion of the universe to speed up, rather than slow down. This unknown force, dubbed by scientists as "dark energy," is analogous to throwing a ball into the air and realizing it is speeding up as it flies into the sky, rather than slowing down and returning. Since dark energy makes up over 70 percent of the universe, understanding this mysterious force is considered one of the top challenges in physics today, according to HETDEX researchers.

The innovative VIRUS system is comprised of 150 small, individual replicas of a single spectrograph. The optical mirrors provided by PG&O for the VIRUS collimator fold mirror were specified for operational wavelength range of 345 nm - 700 nm and are optimized from 350 nm - 590 nm with average reflectivity of greater than 99 percent, and greater than 95 percent between 345 nm - 700 nm. The absolute reflectivity is greater than 98 percent between 350 nm - 590 nm and greater than 92 percent at 345 nm - 700 nm. Angle of incidence is at 12.5±5 degrees. This coating also has to perform in extreme environmental conditions (-25 degrees C to 66 degrees C) and to meet Mil-C-48497 abrasion/adhesion durability standards. The other optical specifications include a surface figure of ?/8 at 632 nm RMS surface quality at 40-20 scratch-dig, and surface roughness of 2 nm RMS.

PG&O provides high performance optical components and thin film coatings for extremely demanding tasks. To meet the requirements for VIRUS, the reflective coatings on borosilicate glass have an operational lifetime of 20 years.

The massively replicated VIRUS instrument will be assembled, aligned, and tested within the Charles R. '62 and Judith G. Munnerlyn Astronomical Laboratory at Texas A&M and in the laboratories of the McDonald Observatory at the University of Texas. Darren DePoy, professor of physics and astronomy and Munnerlyn Laboratory director, and Jennifer Marshall, research scientist, will lead the effort at Texas A&M. Gary Hill, research professor, and Sarah Tuttle, postdoctoral research associate, will lead the effort at the University of Texas.

The astronomical instrument is designed to gather light from distant galaxies and split it into individual spectral wavelengths. The spectrum will reveal an object's chemical composition, its temperature, and the speed at which the universe is stretching between the detected galaxies and Earth. VIRUS will capture spectra from 33,000 points on the sky simultaneously, using fiber optics to transfer the light from the Hobby-Eberly Telescope (HET) focal plane to the huge replicated array of spectrographs. This will permit HETDEX astronomers to produce a 3-dimensional map of a large volume of space, indicating how fast the universe expanded at different periods in history, which will help reveal the role that dark energy has played during different eras. It will search for any evidence that the strength of dark energy changes over time and also will provide the most precise measurement of the geometry of the universe, which is related to the physics of the universe at the moment of Big Bang.

"Our talented and dedicated team includes undergraduate and graduate students from several science and engineering departments and research scientists and engineers in the instrumentation group," DePoy notes. "All of us are excited to be part of such a groundbreaking project." Hill emphasizes that skilled researchers at Texas' flagship universities are working closely together to make the project a success.

DePoy says that because VIRUS is designed for spectroscopic observations of a large number of objects simultaneously, the unique instrument is well-suited to measure the subtle effects that dark energy has on the structure of the universe. Its unparalleled power will also enable a broad range of other astronomy projects.

About Precision Glass & Optics
PG&O has delivered high quality, precision glass, optics, and optical coatings for a variety of applications for over 25 years. The company offers an extensive materials inventory plus a full optical fabrication shop, three large coating chambers, and an expert, in-house engineering staff, for added convenience. Our cost-effective and reliable optics and advanced thin film coatings are ideal for military, aerospace, biomedical, imaging, laser, digital cinema, solar markets, and more. For more information, visit

Funding for the Hobby-Eberly Telescope Dark EnergyExperiment (HETDEX) is provided by the State of Texas, the University of Texas at Austin, Texas A&M University, other partner universities, private donors and the National Science Foundation. The HETDEX collaboration includes the University of Texas at Austin, Texas A&M University, Pennsylvania State University, Leibnitz-Institut fuer Astrophysik Potsdam (AIP), Max-Planck-Institut für Extraterrestrische Physik (MPE), Ludwig Maximillians University, Munich, and Georg-August University, Goettingen. For more information, visit

About Research at Texas A&M University
As one of the world's premier research institutions, Texas A&M is a leader in making significant contributions to the storehouse of knowledge in many fields, including rigorous scientific and technological disciplines. Research conducted at Texas A&M represents an annual investment of more than $689M, which ranks 20th in total research expenditures among all U.S. universities and third nationally for universities without a medical school, according to the National Science Foundation. Research at Texas A&M creates new knowledge that provides basic, fundamental and applied contributions resulting in many cases in economic benefits to the state, nation and world. For more information, visit

SOURCE: PG & O Precision Glass & Optics

PG & O Precision Glass & Optics